The present invention relates to a new herbal formulation, comprising essential oil of medicinal plant Foeniculum vulgare and other plants useful as insecticide against mosquito larvae. The formulation of the present invention has toxic action against larval stages of malarial vector, Anopheles stephensi. The property is attributed to the synergistic combination of essential oil of plant genus Foeniculum vulgare and other essential oils derived from medicinal plants.
Mosquitoes are the single largest group of insects, which transmit many diseases like malaria, filaria, Japanese encephalitis and dengue throughout the world. For the management of vector mosquito population, use of chemical insecticides is now being seriously questioned due to various factors like multiple resistance to insecticides, environmental pollution, and high cost.
Anopheles stephensi Liston type form is a major vector of urban malaria in India (Sharma, 1996). This species essentially breeds in contained water habitats such as overhead tanks, water storage at construction sites, piped water leakages in sluice valve chambers, ornamental fountain tanks, cemented pools, wells etc. (Kalra and Sharma, 1987). Outbreaks of malaria in urban areas due to A. stephensi at the construction sites have been reported (Kumar et al., 1991; Adak et al., 1994). In India, control of urban malaria is carried out under urban malaria scheme (UMS) which is based on anti-larval methods. At present about 46 million population living in 29 cities is under high risk requiring accelerated urban malaria control program.
Every year, there are an estimated 300 million cases of malaria throughout the world. Mortality associated with malaria is estimated at 1.1 million deaths per year (WHO 1999) and is rising in tandem with drug resistance (WHO, 1999; Trape, et al., 1998).
Approaches to reducing the incidence of malaria have focused largely on controlling mosquito populations with chemical insecticides and by physical barrier methods (impregnated nets), or by using drugs to prevent infection with malarial parasites (Plasmodium spp).
The continued use of chemical insecticides results in the gradual building up of resistance in mosquitoes as well as in environmental pollution. Chemical insecticides are toxic to the non-target natural predators of mosquitoes, which co-exist with the mosquito larvae. Alternatively, biological control agents, such as larvivorous fish, have been successfully used under bioenvironmental methods for the persistent control of mosquito breeding (Sharma 1986).
The problems presented and created by the spraying of chemical insecticides in malaria control has made it imperative to develop alternate methods of vector control. Biocides offer many advantages over chemicals i.e., high specificity, biodegradability, safety to environment, low cost and in some cases recycling properties, these characteristics make the biocide an important and useful tool in integrated vector control program.
Most mosquito control programs aim at larval stages as a target in their breeding sites with larvicides, because adulticides may only reduce adult populations temporarily allowing for rapid upsurges within a few days. Kettle (1995) pointed out that control of immature stages of mosquitoes has traditionally been effected by the application of insecticides as solution in oils, as an emulsion, wettable powders or dusts. However, these have been achieved with the inherent risk of contamination of water used for domestic purposes especially in rural areas where this water provides excellent breeding conditions for mosquitoes. Due to the dramatic increase in resistance of mosquitoes to familiar chemicals in the absence of new compounds, better alternative means of control are sought. The urge for this has increased, especially after recent public awareness of potential hazards emanating from the widespread use of insecticides (Busvine and Pal, 1969; Curtis and Pasteur, 1981; WHO, 1987). One alternative is the use of plant extracts as botanical insecticides (Arnason et al., 1989). A considerable number of plant derivatives have been shown to be effective against a wide array of insect species (Schumutterer, 1990; Elhag et al., 1996; Wilps, 1995; Amorose, 1995), but very few have been reported for larvicidal action against mosquitoes e.g. dichloromethane extract of Abuta grandifolia and Minthostachys setosa against larvae of Aedes aegypti, a mosquito vector of dengu fever (Ciccia et al., 2000) and seed extract of Atriplex canescens against larvae of another mosquito species, Culex quinquefasciatus (Ouda et al., 1998).
There is no record of resistance to whole-plant extracts, possibly due to the synergistic action of many constituents: isolation and administration of a single active agent greatly facilitates the evolution of resistance in parasites (Chawira, et al., 1986) and mosquitoes. It is possible that phytotherapy produces fewer adverse effects than chemotherapy, because there are many active agents, each at a smaller dose than that required when a single agent is administered.
Foeniculum vulgare Mill syn. F. capillaceum Grilib is a aromatic herbaceous plant known locally (in India) as fennel and used as culinary spice. The fruits are aromatic, stimulant and carminative. Official pharmacopoeias of various countries throughout the world list this plant for use in diseases of the chest, spleen and kidney. Fennel is a constituent of liquorice powder and preparation for allaying gripping. F. vulgare has been reported to exhibit many pharmacological effects including antibacterial activity (Ruberto et al., 2000) and toxicity towards stored grain insects (Kim and Ahn, 2001). It is useful in infantile colic and flatulence (Purthi, 1976). In spite of considerable pharmacological studies carried out world wide on F. vulgare fruits survey of scientific literature showed that the essential oil of F. vulgare has not been evaluated against insect vectors of public health like mosquitoes. The applicants have carried out preliminary experiments on essential oil of the fennel fruit (Foeniculum vulgare) to explore whether it possesses any toxic and/or behavior modifying effects towards malarial vector, A. stephensi (Liston).
Hitherto known insecticides to control of malarial vector at larval stage are malariol oil, temephos and fenthion, and are being commonly used in anti-larval operations but all these compounds are also toxic to co-existing beneficial organisms.
Hitherto known some plant products have been demonstrated to be effective against mosquitoes (Wilps, 1995; Elhag, 1996). Example include Syzygium aromaticum (L.) (Hassanali et al., 1990), Curcuma raktakanda (Latha and Ammini, 2000), Hydrocotyle jaranica Thunb. (Venkatachalam and Jebanesan, 2001), and Azardirachta indica A. Juss. (Elhag et al., 2001; Prasad, et al., 2001).
During the course of our research, in an attempt for preparing insecticides from natural products, the applicants have found that the essential oil of a medicinal plant, Foeniculum vulgare and other plant either singly or in combination can be employed for controlling mosquito, Anopheles stephensi. 
The technical ingredient used in the present invention, essential oil of F. vulgare is reported in the literature for toxicity towards insect-pest but not towards A. staphensi. 
The main object of present invention is therefore to provide a composition of essential oils as an herbal larvicide useful in killing mosquito larvae and obviates the drawbacks as detailed above.
Another object of the present invention is to provide a composition of the plant essential oils as an herbal formulation useful as larvicide for the control of mosquito larvae, which is safe, cheap, biodegradable, environmentally friendly, without any residual effect and commercially viable.
Another object of the invention is to provide a composition, which is miscible with water enabling it to be compatible with other microorganism present in water.
Accordingly the present invention provides a composition useful as an insecticide or larvicide, particularly against mosquito larvae which comprises blending the essential oil extracted from the plant genus Foeniculum vulgare with one or other essential oils of medicinal plants.
The basis for which the invention has been developed is due to our finding that when essential oil of Foeniculum vulgare is mixed with one or other essential oils of medicinal plants; the resultant composition develops insecticidal property, which is especially active against mosquito larvae. The water miscibility as an additional advantage with the use of essential oil makes the invention more superior than commercially available insecticides which only floats on the water surface thereby cause suffocation to other water inhabiting organisms by depleting the oxygen level in the water. Accordingly, the composition is useful as larvicide for the control of mosquitoes.
Accordingly, the present invention provides a novel synergistic herbal insecticidal formulation against mosquito larvae, said formulation comprising:
(i) essential oil derived from plant Foeniculum vulgare 0.01 to 2.6 wt. %,
(ii) essential oil(s) derived from one or more plant sources 0.01 to 2.6 wt. %,
(iii) emulsifier or combination of emulsifier 0.01 to 3.8 wt. % and,
(iv) balance water as a carrier or diluent.
One more embodiment of the invention relates to a synergistic formulation, wherein the essential oil(s) from other plant(s) is/are selected from plants belonging to families Apiaceae, Geraniaceae, Lamiaceae, Meliaceae, Myrtaceae, Poaceae and Zingiberaceae.
Another embodiment, the essential oils used can also be extracted from different plants selected from Eucalyptus citriodoora, Foeniculum vulgare, Mentha spicata var. viridis, Mentha arvensis, Mentha piperita, Ocimum basilicum, Cymbopogon species, Pelargonium graveolens and/or Zingiber officinale or mixtures thereof.
Still another embodiment, emulsifier used for preparing the formulation may be ionic, non-ionic or mixtures thereof, selected form group consisting of Soya lecithin, Tween-20, Tween-80 and Triton-X.
Yet, another embodiment of the invention relates to the activity of the formulation against mosquito larvae of various mosquito species selected from Aedes aegyptii, Anopheles stephensi, Anopheles quadrimaculatus and Culex species.
Yet another embodiment of the invention relates to the essential oils which are selected from Foeniculum vulgare in the range of 0.01 to 2.6 wt. %, Mentha spicata var. viridis in the range of 0.01 to 2.6 wt. %, and Zingiber officinale in the range of 0.01 to 2.6 wt. %.
Yet another embodiment of the invention relates to ratio of essential oils of plants Foeniculum vulgare: Mentha spicata var. viridis:Zingiber officinale which is in the range of 1-7: 1-5: 1-7.
Yet another embodiment, preferred ratio of essential oils of plants Foeniculum vulgare: Mentha spicata var. viridis:Zingiber officinale used is in the range of 3-7: 1-5: 3-7.
Yet another embodiment, the said formulation is having synergistic activity against the mosquito, wherein mean mortality of mosquito larvae is up to 94%.
In another embodiment of the invention provides a herbal formulation useful as insecticide against malarial vector, mosquito which comprises of 0.01 wt. % to 2.6 wt. % of essential oil derived from plant genus Foeniculum vulgare and 0.01 wt. % to 2.6 wt. % of one or more essential oils of plants and 0.01 wt. % to 3.8 wt. % of tween-80 or combinations thereof belonging to plant family Apiaceae, Geraniaceae, Lamiaceae, Myrtaceae, Meliaceae, Poaceae and Zingiberaceae.
In an embodiment of present invention, has several components which include formulation in the form of liquid which is fit for use in water logging conditions and can be used any time by mixing it with water and tween-80, an emulsifying agent. It is non-toxic to human beings, parasite and predators. The present invention thereby provides for the preparation of an insecticidal formulation which when used provides complete killing of mosquito larvae. The response is the result of insecticidal property of the composition-enabling killing of target insects.
The preferred composition of the present invention consists of essential oil of plant genus Foeniculum vulgare, Mentha spicata viridis and Zingiber officinale and Tween-80 purchased from Hi-Media, Mumbai. The amount of these components may range from 1:1:1 to 3:5:7.